HOW DOES IT WORK
(This is partial a summary made from the migration-counting
methods developed bij the LWVT1 in the beginning of the eighties)
Lit: LWVT 1985. Handleiding tellen van zichtbare vogeltrek. Rapport,
My countingpoint is on an arbitrary location in the Netherlands,
close at my home so I don't have to travel to far on the bike, and on a
relative quiet place so you can hear the birds calling. Because of this
arbitrary place in the inland, the birds I count are part of the visible
In autumn most birds migrate in the morning. 50% of birdnumbers
(in autumn) migrate in the first 2.5 hours of the day. By using that part
of the day for counting you can get a rather good idea of the migration
that season. Not all species use the morning to migrate. The best example
of daytime-migration are the larger raptors. But also Barn Swallow, House
Martin, Swift, Skylark, Jay, Tits, Gulls, are typical birds of which the
largest part of migration take place during the late morning and daytime.
In spring average migrating-time is later than in autumn. Perhaps
due to having the wind behind one. Thus birdmigration also occurs in spring
and can be really spectacular (I have no time for counting that). The way
of counting and the dividing of countingperiods during the day in periods
is the same as in autumn. Actually, birdmigration is a phenomenon which
occurs the whole year but is on most places best visible in autumn.
Just counting on different times of the day gives you an idea
of the birdmigration, but when you want to compare one counting with an
other counting that season, with countings in other year or at other places,
you must have data which you can compare. Because of that, the daylighthours
have been split into four parts: early morning; late morning, daytime and
The countings which you find on this website are mostly early morningcountings.
One counting exist of 10 periods of 15 minutes counting. Every counting
starts 30 minutes before sunrise en stops 2 hours after sunrise. The period
of the late morningcountings takes an other two and a half hour
after the early morningcountings. The
eveningcountings starts two
hours before sunset and last until half an hour after sunset. The restperiod
of countings during the day is called
daytime and here the periods
are separated in hours.
|Example of countingperiods
30-sep-2001 and the numbering of the countingperiods
Ten periods of 15 minutes
07.05 - 09.35 h
Ten periods of 15 minutes
09.35 - 12.05
One period of 55 min.
12.05 - 17.14 h
Four periods of one hour.
One period of 14 minutes
Ten periods of 15 minutes
17.14 - 19.44 h
What is written down:
To find out which direction birds fly, I write down the flight-direction
in the "16 different directions". Sometimes you only hear a bird
pass by but you can't find it. These birds don't get a direction on paper;
they are only "heard". Other birds don't show a very clear direction
while migrating. They are soaring or whirling to higher airlayers. These
birds get an "indefinite direction"
Birds can pass very close, but also fly high or far away while migrating.
Large birds can be seen more than a kilometer away, large groups of geese
for example can be detected on several kilometers. When counting with more
than one person, people start to look farther and will detect more birds
than when you are counting alone and already have problems to detect and
counting all the birds flying over your head. Because of that there is
the distinction between close flying birds and birds far away. The border
of that is a circle around the counting point of 100 meters. Every bird
outside that circle (> than 100 meters away) get the notice "outside".
Mostly I count alone. This is (can) be a problem. When there is a lot
of migration you have to write a lot. For example 20-okt-2001, I counted
five hours and I wrote seven pages (A5) full with data. It takes to much
time to write birds down and you get crazy of the change writing - looking
to birds - write - look - write - etc. For that reason mostly I speak
in the observations in a memo-recorder. I use a Sony instead of Philips
(because this memo doesn't use power when "pausing".) and work it out later.
I write it down on paper and put it in a database later on.
"Every group or even every solitairy migrating bird, get its own notice
and is put in a database".
Example of data-input:
Species (Soort) - Direction (Richting) - N (N) - "outside" (b)
- Period (K) - Date (data) - Comment (Bijzonderheden)
In the end there will be a database as shown above in which
every group of migrating birds is mentioned; species, direction, number,
distance, time and date.
What to do with this data??
|The most fun of birdcounting of course is watching
the birds pass by ( ....or go to Falsterbo to get your kicks... ) and comparing
the numbers with other countings, earlier years or other places. At this
moment I put the the totals of the early-morningcountings on the World
Wide Web. When I want, it is (thanks to the database) quite easy to produce
diagrams of the different species, for example:
when do they migrate in the season
At what time in the morning do they pass
What is their average the flight-direction
What is the average group-size
Difference between years and months.
But there are already lots of early morningcountings (also on other
locations) I did at the moment (more than 300), and it is going to be more
and more next weeks/years. Perhaps in the future-years everyone can make
it's own queries of this data on the internet (That can take some time
still). For the moment you can find here only daily lists of species and
1: LWVT = Landelijke Werkgroep Vogeltrek Tellen (which
means such as "Dutch Working-group Birdmigration Countings").